1. Field of the Invention
The instant invention relates to a magneto-optical recording medium and an information recording method using the same, with which information is recorded by forming a bit of a reversed magnetic domain using a laser beam and an external magnetic field, and information is read out by utilizing a magneto-optical effect obtained upon radiating a polarized laser beam and, more particularly, to a magneto-optical recording medium and an information recording method using the same, which perform an over-write operation by a magnetic field modulation method.
2. Related Background Art
Conventionally, as a rewritable high-density recording method, a magneto-optical recording method has received a lot of attention. With this method, information is recorded by writing a magnetic domain in a magnetic thin film, and the recorded information is read out by utilizing a magneto-optical effect.
Since the magneto-optical recording method uses a magnetic member on a disk as a recording medium, it has features that the recording medium is exchangeable, and information is rewritable.
Such a conventional magneto-optical recording method requires three recording processes (to erase old data, to record new data, and to check whether or not new data is properly recorded). For this reason, in order to rewrite information, a disk must be rotated three times, and hence, the time required for rewriting information corresponds to three revolutions of the disk.
In recent years, over-write methods (an optical modulation method and a magnetic field modulation method) with which new data is directly recorded on old data without executing the erasing process of the three recording processes have been proposed and extensively examined. Of these methods, the optical modulation method performs recording by forming a bit using a modulated laser beam. However, in consideration of the Gaussian distribution of the laser beam intensity and the temperature distribution of a magneto-optical recording medium, the allowable range of laser power for forming a magnetic domain with a small diameter is very narrow with respect to a given beam size. Furthermore, when the magnetic domain interval (bit interval) is decreased to increase the density, a temperature rise of a medium caused by the laser beam which was radiated immediately before a current recording operation adversely affects the current recording. More specifically, when a random pattern is recorded, the optimal value of laser power undesirably changes depending on the pattern.
In contrast to this, since the magnetic field modulation method does not easily pose the above-mentioned problems caused by the temperature distribution although it requires a rather complicated apparatus arrangement, it has been considered promising for practical applications, and has been developed extensively.
When an over-write operation is performed by the conventional magnetic field modulation method, a high-frequency magnet must be generally used as an external magnetic field application means to reverse a magnetic field upward or downward in a direction perpendicular to the film surface in correspondence with a digital data signal "1" or "0".
In this case, when the reversing speed of the magnetic field is increased, the magnetic field that can be applied tends to decrease, and therefore the data transfer speed is limited. Also, since the magnetic field decreases, the magnetic head must be arranged sufficiently close to a medium, and the medium or the head may be damaged due to a contact between them.